Retoning carrier beads in the development zone

ABSTRACT

A development method wherein developer, comprising a mixture of toner particles and carrier beads, is lifted from a trough or sump and is cascaded over the surface of an insulating plate bearing a latent electrostatic image and the toner is attracted from the carrier to the plate to develop the latent image thereon. The carrier beads are retoned with toner particles from a container located in the development zone as the beads give up toner particles to the plate during the development process. The carrier beads and residual toner particles are directed to the trough where additional toner particles are then added to the mixture, whereupon the returned carrier beads are again lifted from the trough and cascaded over the insulating plate to start the same cycle over again.

United States Patent 1191 Weiler 1451 Feb. 5, 1974 1 RETONING CARRIER BEADS IN THE 3,532,071 10/1970 Mc Carroll 118/637 DEVELOPMENT ZONE 3,542,579 11/1970 Gundlachu 118/637 3,648,658 3/1972 Weller 117/175 [75] Inventor: Ernest A. H. Weiler, Rochester,

Primary Examiner-William D. Martin [73] Assignee: Xerox Corporation, Stamford, Assistant Examiner-M. Sofocleous Conn. Attorney, Agent, or Firm-Paul M. Enlow et al. [22] Filed: Aug. 5, 1971 211 App]. No.: 169,400 [57] ABSTRACT Related Us. Application Data development method wherein developencompris- 1 mg a mixture of toner particles and carrier beads, 1s [62] 85 87040 Sept' 1969 lifted from a trough or sump and is cascaded over the surface of an insulating plate bearing a latent electrostatic image and the toner is attracted from the carrier [52] US. Cl 117/17.5, 113849317; to the plate to develop the latent image thereon. The Int Cl 13/08 15/08 carrier beads are retoned with toner particles from a [58] Fieid Ian/1785 H8/637 56/ container located in the development zone as the 355/3 beads give up toner particles to the plate during the development process. The carrier beads and residual References Cited toner particles are directed to the trough where additional toner particles are then added to the mixture, UNITED STATES PATENTS whereupon the returned carrier beads are again lifted 3,685,486 8/1972 Donalies 117/17.5 from the trough and cascaded over the insulating plate 3,611,991 10/1971 Young 117/175 t s art the same cycle over again. 3,396,700 8/1968 Donalies 1l7/l7.5 3,393,663 7/1968 Donalies 118/637 1 Claim, 2 Drawing Figures PATENIEB FEB 51974 INVENTOR. ERNEST A. H. WEILER ATTORNEY This is a division of application, Ser. No. 858,040, filed Sept. 15, 1969, now-U. S. Pat. 3,648,658.

BACKGROUND OF THE INVENTION ble, or developed, with a colored powderous material,

such as in the process of xerography, it is desirable to deposit the powderous material on the plate so that it adheres only to the image areas of the latent image to form a clear, well defined, visible image. One method of depositing toner on the plate is by cascade development techniques. In cascade development a developer mixture, comprising a finely-divided, pigmented, electro scopic. powder referred to as toner and a coarse,-

granular material referred to as carrier beads, is cascaded from an elevated position over the surface of the plate bearing the latent image. The carrier beads are made or are coated with a material which is removed from the toner material in the triboelectric series so that when the two are mixed together to form the de veloper mixture, the toner particles are triboelectrically attracted to the carrier beads. The toner particles are small relative to the-carrier beads and many toner particles are .carried throughout the development system by each carrier bead. AS'the developer flows across the plate bearing the latent image in the development zone, the electrostatic charges on the plate attract toner particles from their respective carrier beads onto the plate surface where they are deposited. in imagewise configuration. It is common practice to use a development electrode in the development zone when depositing toner on the plate through cascade development techniques to improve solid area coverage. The

effect of such an electrode-is to change the field configuration of the electrostatic image and increase the field in the space above solid areas of charge.

As a result of giving up toner particles to the plate during cascade development, the carrier beads, become under-toned while still in the development zone; that is, a given carrier bead becomes under-toned when it has less toner attracted to it through triboelectric action than if an unlimited quantity of toner particles were available to it. The presence of under-toned carrier beads in the development zone is undesirable since less toner particles are available to be deposited on the plate than there would be if each carrier bead maintained in a fully-toned condition throughout the development zone; that is, when a carrier bead has attracted to it all the toner particles that it can through triboelectric action when it has an unlimited supply of toner particles available to it. The under-toned condition is a common occurrence in cascade development systems, particularly in the lower regions of the development zone since more toner has had a chance to transfer from the carrier beads to the plate.

To provide more toner particles throughout the development zone of a cascade system, the development zone is usually made long enough to assure that enough toner is cascaded over all parts of the plate to fully develop the latent image thereon.

ln reproduction-systems such as those using a reusable insulating plate in the shape of a drum which is ro- I tated continuously through several processing stations arranged about its periphery, the area available for the development zone is necessarily limited to only a portion of the drums periphery. Because the development zone is limited in length and because a relatively large amount of toner is necessary to be cascaded through such a development zone to adequately develop the latent image, the speed at which the drum rotates is restricted to lower values which, in turn, restricts the speed of the entire reproduction process. On the other hand, if additional particles could be added to the developer mixture throughout the development zone to maintain the carrier beads in a more nearly fully-toned condition in all areas of the development zone, more toner would 'be available for deposit on the plate and the development zone could be shortened and the plate in such a continuous system could rotate at a much faster speed than known heretofor. It is obvious that this would make amuch faster reproduction system.

The present invention is an apparatus for supplying additional toner particles, as needed, to carrier beads system. The apparatus includes an apertured develop-.

ment electrode placed adjacent the development zone having a container of toner particles attached thereto. The device places additional toner particles in the apertures of the electrode and a under-toned carrier beads passes adjacent to and/or strikes the electrode, additional toner particles at the electrode are attracted to the carrier beads until they become fully-toned again. This acquisition of toner particles by the under-toned carrier beads occurs throughout the development zone thereby minimizing the effects of the toner particles on the carrier beads beingused upon the plate to result in excessvely under-toned carrier beads in the lower region of the development zone. v

Accordingly, it is an'object of the'invention to improve the development of latent electrostatic images.

It is a further object of the invention to improve apparatus for cascade development of latentelectrostatic images. I i I his a further object of the invention to improve apparatus for cascade development by supplying additional toner particles to the carrier beads in the development zone as needed during the development process.

It is a further object of the invention to improve cascade development-by.supplying additional toner particles tocarrier beads through an apertured development electrode containing a reservoir of toner particles while the carrier beads flow through the development zone.

SUMMARY The present invention includes an apertured development electrode spaced at-a gap from the plate being deto participate in the developing process until they leave the development zone.

BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding of the invention as well as other objects and further features thereof, reference is had to the following detailed description of the inven- ,tion to be used in conjunction with the accompanying drawings wherein:

FIG. 1 is a schematic illustration of the invention. FIG. 2 is a detailed view of the development electrode.

DESCRIPTION OF THE PREFERRED EMBODIMENT The present invention can be adapted to any reproduction apparatus which uses electroscopic pigmented powders, or toner, to develop an electrostatic latent image. For the purpose of this disclosure, however, the invention will be described within the environment of a xerographic reproduction apparatus.

Referring to FIG. 1 there is shown a continuous xerographic copier, having a photosensitive plate 60 on which a latent electrostatic image of the information to be reproduced is formed. The plate is in the shape of a rotatable drum-63 which is driven by shaft 64. The peripheral surface of the drum is covered with layer 62, an electrically conductive material, which, in turn, is covered on its outer surface with layer 61, a photosen sitive insulating material such as vitreous selenium.'The drum has five processing stations located about its per'iphery which carry out the steps of the xerographic process. These stations include charging station 10, exposing station 20, developing station 30, transfer station 40, and cleaning, station 50. I

A latent electrostatic image is formed on the drum by passing its surface through charging station 10 and exposing station 20. The charging stationconsists of any suitablemeans for placing a uniform charge on layer 61 such as the corona charging device 11 shown in the drawing. Exposing station 20 comprises projector 21 which projects and focuses a light pattern on the drum conforming to the image to be reproduced by the xerographic system. The image projected onto the photosensitive layer of the drum which, synchronized with the movement of the photosensitive layer of the drum, causes selective charge dissipation on elemental areas of layer 61- to form a latent electrostatic image thereon. Other means for forming electrostatic images including means for forming on ordinary insulating surfaces are known in the art and may be used instead of the one shown.

After the formation of the latent electrostatic image by passing the drum through stations 10 and 20, the drum carries the latent image to developing station At the developing station a developer mixture comprising toner powder and carrier material is cascaded over I the drum surface and the toner particles are attracted to and deposited on the drum surface in imagewise configuration. The toner particles are'comprised of pigmented, resinous, electroscopic powder while the carrier material, commonly referred to as carrier beads, is a coarse, granular material which is removed from the toner in the triboelectric series or is coated with a material which is removed from the toner in the triboelectric series. When the'toner and carrier beads are mixed, several toner particles are attracted to each grossly larger carrier bead through triboelectric attraction. Then, when the developer mixture is cascaded over the surface of the drum, toner particles are attraced from their respective carrier beads and deposited on the surface of the drum by electrostatic charge pattern on the drum.

The cascade development assembly comprises housing 31 containing a quantity of developer. The mixture is lifted to an elevated position over the drum by buckets 34 which are supported on conveyor'33 which, in turn, is supported and driven by pulleys 35. The developer mixture lifted to the elevated position over the drum surface is dumped onto the drum surface in the vicinity of deflector plate 37. The deflector plate directs the developer mixture onto the surface of the drum where it flows across the surface through the 'development zone 30 and then into the trough 38 of housing 31. The development zone includes a development electrode shown in greater detail in FIG. 2, which is spaced at a gap from the surface of the drum. Attached to the development electrode is toner reservoir 70 including a container 71 which contains a quantity of toner particles. Also within the container 71 is at least one and preferablya plurality of toner agitators '73 which keep the toner particles in a loose, free-flowing consistency. Development electrode 74 contains a plurality of apertures through which toner particles within housing 71 can be placed on and/or adjacent the development electrode. During the development process developer. flows across the surface of drum 60 between the drum surface and development .electrode and carrier beads in the developer mixture give up toner particles which are deposited on the drum surface. The carrier beads are then retoned with additional toner particles asthey flow adjacent and/or incontact with the development electrode.- This retoning process will be described in more detailbelow.

Following the development step, the'drum carries the developed image through transfer station 40 where the toner imge is transferred from the drum surface to support material 41. Transfer of the developed image onto the support material is aided by corona device 41 which applies an electrostatic charge to the support material having a polarity opposite that of the triboelectric charge on the toner particles. Transfer takes place between guide rollers which act to position the support material against the photosensitive drum at the transfer station. Support material 41 is fed from reel 43 before transfer and is rewound on reel 44 after transfer takes place. If the support material is the permanent substrate upon which the developed image is to be fixed, fusing device 46 is desirable and should be placed along the path of this support material between the point where the developed image is transferred to the support material and the point where the support material is rewound on reel 44, The fusing device is positioned to heat the toner particles thereby permanently fixing them to the support material. 1

The final station shown in the drawing is cleaning station 50 comprising a cylindrical fur brush 51 which contacts the photosensitive surface of the drum. The cleaning station is utilized to remove any residue toner particles from this photosensitive surface after transfer occurs and before a new imaging cycle is begun. It is intended that various moving elements by driven by any suitable means-For instance, the motor that drives drum 63 can also through appropriate gearing drive all the other moving elements in the copier.

It is within the confines of the development station, station 30, that the present invention is utilized. Toner particles 72 are placed in container 71 and are supported by the container adjacent the apertures 75 in development electrode 74. During the developing process developer is elevated to a position over the drum by the buckets 34 and then released so that it flows through the development zone between the drum surface and development electrode 74. As developer flows across the drum surface toner particles are attracted away from .the carrier beads and adhere to the plate in imagewise configuration. The carrier beads are fullytoned or nearly'fully -toned when entering the development zone and, as they give up toner particles to the drum surface, during the cascade process, they become under-toned. For the purpose of this disclosure, a fullytoned carrier bead is one which has all the toner particles attracted to it due to triboelectric action that it can when an unlimited supply of toner particles is available and the developer mixture is thoroughly mixed and an under-toned carrier bead is one which has less toner on it than when fully-toned, particularly when'toner particles have been attracted from the carrier beads to the drum surface in the development zone. A carrier bead, after becoming undertoned, continues to'flow through the development zone and in so doing moves adjacent and/or in contact with the development electrode. The under-toned carrier bead, in so doing, attracts toner particles from the apertures in the development electrode and becomes retoned; that is, it becomes more nearly fully-toned. This process can continue until the carrier beads finally exit the development zone and enters the trough 38 of housing 31. After entering the trough, the carrier-beads are 'mixed with additional toner particles before being elevated again.

The development electrode, in addition to adding toner particles to the cascading developer mixture as needed, improves the deposition of toner on the plate,

especially in solid areas. The development electrode causes the lines of force from the image areas to be directed in generally parallel relationship towards the development electrode and in perpendicular relationship to the image surface and to the development. electrode. This results in a uniform adherence of the toner over the image area and produces a uniformly dark or concentrated image with lines that are not diffused, as con-' trasted with developing procedures in which there is no development electrode. In the absence of a development electrode the lines of force from the edges or outer portions of an image-area are consequently directed in curved paths to the adjacent discharged or.

background areas, resulting in the lines of force being dissipated from the image areas and producing black or dark effects around the edges and light or white effects at the central portions. Due to the action of the development electrode, solid area toner coverage is improved greatly.

The principle upon which the instant invention in based isas follows. A carrier bead exhibits an attractive force on toner particles due to the relative locations of the carrier bead and toner particle on the triboelectric scale. As carrier attracts toner to its surface it electrostatic attraction for additional toner decreases in proportion to the amount of toner already being held on its surface. Once the carrier can electrostatically accept no more toner it is said to be fully-toned. During the developing process, toner particles are attracted away from the carrier and adhere to the drum surface.

This migration of the toner particles is possible since the attractive force of the image areas of the drum is stronger than the attractive force of the carrier on the particles. A carrier bead which gives'up toner to the drum surface is said to be under-toned and has capacity to attract more toner particles until it again reaches its fully-toned condition. As an under-toned carrier bead force of the carrier beads to retone the carrier beads.

The toner particles in the toner container 71 remain in the vicinity of the development electrode and do not fall into the development zone due to the attractive forces between the toner and development electrode. As the carrier attracts additional toner, its force for at,- tracting toner particles decreases until the force of the development electrode for the toner particles is approximately equal to the force of the carrier beads on the toner particles. At this time thecarrier beads are retoned for further development and do not accept additional toner. The carrier then can move into contact with the latent image and continue to fully participate in the development process.

development electrode aids in triboelectrically charging the toner while maintaining its primary function of controlling the deposition of toner particles on the plate in irnagewise configuration. In the alternative, carrier beads can be mixed with the additional toner in container 71 to triboelectrically charge the toner and to keep the toner in a loose consistency. The toner particles would then he attracted from fully-toned carrier beads in container 71 through the apertures to undertoned carrier beads in the development zone.

In addition to the apparatus outline above, many other modifications and/or additions to the invention will be readily apparent to those skilled in the art upon reading this disclosure and these are intended to be encompassed within the invention disclosed and claimed herein.

What is claimed is: 1. A method for developing a latent electrostatic image on a photosensitive surface with toner particles comprising:

a. cascading carrier beads having toner particles triboelectrically attracted thereto across the photosensitive surface in a development zone whereby the electrostatic charges on the photosensitive surface attract the toner particles from the carrier beads to the surface thereof causing the carrier beads to become undertoned while still in the development zone,

b. retoning the under-toned carrier beads in the de- UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION 3, 790, 97 Dated February 5, 1974 Patent No.

Inventor) Ernest A. H. Weiler It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, Column. 8, Line ll, after the word "sensitive",

insert -surface to-.

Signed and sealed 17th day of September 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. I c. MARSHALL DANN Commissioner of Patents Attesting Officer USCOMM-DC 60376-P69 i U,S. GOVERNMENT PRINTING OFFICE: 19! 0-366-334,

FORM PO-1050(10-69) UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION February 5, 1974 v Patent No. U Dated Inventor( A. H.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Claim 1, Column 8, Line ll, after the word "sensitive",

insert -surface to-.

Signed and sealed this 17th day of September 1974.

(SEAL) Attest:

McCQY M. GIBSON JR. C. MARSHALL DANN Attesting Officer Commissioner of Patents USCOMM-DC 6O376-P69 U,S, GOVERNMENT PRIN'HNG OFFICE: 1969 0-366-33l,

FORM PO-105O (10-69) 

